The abundance and habitat preference of small mammals in the udzungwa ecosystem, Tanzania.

Studies on small mammal abundance and habitat preference were carried out in some habitats within the Udzungwa ecosystem, during the wet and dry seasons of 1997 and 1998. Small mammals were sampled using two types of kill traps (metal snap traps and museum special traps) and two types of live traps (pitfall traps and Sherman traps). In total 12320 trap nights and 1760 bucket nights were realised. This trapping effort yielded 372 individuals of small mammals, 82% of which were 11 species of rodents and the remainder being insectivorous species. Eleven more species were recorded from ad libitum studies. Non-target animals, which included amphibians, birds, reptiles and invertebrates, were accidentally caught during the survey; most of the accidental captures involved pitfall traps. Frogs were caught in all the four trap types used in the study plots. Traps varied in efficiency with which they caught the small mammals. Among non¬pitfall traps the museum specials were the most efficient; this trap type ranked first in the number of animals caught by every 100 trap- nights. Pitfall traps were most efficient (90%) in catching the light small mammals. Traps efficiency also varied through trapping period. Specimens obtained from kill traps were commonly found ruined, where the trap and or scavengers destroyed animal body parts, as such, some important information were usually missed. Some trap locations had higher frequency of small mammal captures than others, mammals caught from such spots within a period of less than twenty four hours were dominated by individuals belonging to the same species. This suggested that intra¬specific association among individuals were most common. Association between individuals of opposite sexes varied on temporal basis, there were more male to female associations during the wet season than during the dry season. This type of individual association was in favour of the breeding (wet) season. The multimanunate rat (Mastomys natalensis) was commonly trapped at 1000 masl in the forest interior. Since the rats are known to occupy habitats associated with human settlements, the results suggest that although no human inhabited areas were currently found in the Udzungwa forests, there had been human settlements in the Udzungwa forests as high as 1000 masl. The abundance of small mammals in the forest was higher where grass cover was founc to dominate the ground cover. On the lowlands, human disturbance of the forest habitat reduced small mammal: diversity. Where such disturbances had encouraged crops, Mastomys natalensis was found to dominate other small mammals; such habitat types supported the highest small mammal biomass. In the montane rain forest the most numerous small mammals were the Crocidura shrews. Multimammate rats (Mastomys natalensis) were the most abundant rodents in the study area (Udzungwa ecosystem); this species was found to dominate small mammals on the lowland (250 masl). The species was most abundant, in cultivated habitats where the highest small mammal live-weight was recorded. Small mammals were more numerous during the wet season when reproduction was also found to be at its peak. Sex ratio seemed not to affect reproduction potential